Electrophotographic fusing apparatus

ABSTRACT

Apparatus for preventing toner and other particulate material from contaminating the fusing station in an electrophotographic apparatus. Means are provided for forming a protective air curtain between the fusing station and the path along which a toner-bearing support travels during the fusing operation, whereby toner and other particulate material separated from the support are intercepted before contacting and thereby contaminating the fusing station. The invention is particularly adapted for use in electrophotographic apparatus of the type in which fusing of the toner image to a receiving sheet is accomplished by passing the receiving sheet with its toner image facing downward overtop a source of thermal energy.

United States Patent Laisney Oct. 24, 1972 541 ELECTROPHOTOGRAPHIC FUSING Primary Examiner-Charles J. Myhre APPARATUS Attorney-R. W. Hampton, P. R. Holmes and W. W. [72] Inventor: Alexis D. Laisney, Rochester, N.Y. Kurz [73] Assignee: Eastman Kodak Company, [57] ABSTRACT Rochester Apparatus for preventing toner and other particulate [22] Filed: Feb. 5, 1971 material from contaminating the fusing station in an electrophotographic apparatus. Means are provided [211 112900 for forming a protective air curtain between the fusing r station and the path along which a toner-bearing sup- [52 us. Cl. ..263/6 E P travels during the fusing operation, whereby 51] Int. Cl. ..G03g 13/20, G03g 15/20 toner and other Particulate material separated from 58 Field of Search ..263/6E;219/388 the Support are intercepted before Contacting and thereby contaminating the fusing station. The inven- [56] References Cited tion is particularly adapted for use in electrophotographic apparatus of the type in which fusing of the UNITED STATES PATENTS toner image to a receiving sheet is accomplished by Q r passing the receiving sheet with its toner image facing 3,448,970 6/1969 Kollbas ..263/6 E x downward ovemp a some ofthermal energy 3,498,592 3/1970. Moser et a1. ..263/6-E 8 Claims, 1 Drawing Figure 1 i j /2 PAPER TRANSFER FEED/N6 CL EA/W/VG CHA RG/NG EXPOSURE DE VE L OPl/VG PATENTED UN 24 I972 ALEX/5 0. LA/S/VE) INVENTOR.

I BY m AGE/VT ELECTROPHOTOGRAPHIC FUSING APPARATUS The present invention relates to electrophotographic reproduction apparatus and particularly to apparatus for fusing a toner image upon a surface on which the image has been loosely formed.

Formation and development of electrostatic images in accordance with the principles of electrophotography are well known. Briefly and generally stated, an electrostatic image is formed by uniformly charging the surface of a photoconductive material and imagewise exposing the charged surface with suitable radiation as to selectively dissipate the uniform charge in accordance with the image. Development of the electrostatic image so formed is accomplished by contacting the image with colored electroscopic particles, commonly known as toner, which adhere to the image by electrostatic attraction. The developed image can then be fused directly to the photoconductive surface to form a permanent record, or, should it be desired to reuse the photoconductive material, the image can be transferred to a paper-receiving sheet on which the image can be subsequently fused. Transfer of the toner image to the receiving sheet is commonly efiected by bringing the receiving sheet into contact with the toner image and subjecting the area of contact to a corona discharge which causes the toner to be repelled from the photoconductive material and attracted toward the receiving sheet. Fusing the toner image to its supporting surface is commonly accomplished by subjecting the image to a source of thermal energy, such as an infrared lamp, which serves to momentarily liquify the toner and thereby permit it to penetrate the pores of its supporting surface.

Machines for automatically carrying out the electrophotographic process generally comprise a plurality of processing stations arranged adjacent a predetermined path along which the photoconductive material and/or paper-receiving sheets are caused to travel, each station performing one of the steps comprising the electrophotographic process. Desirability of a particular machine configuration sometimes dictates that the source of thermal energy used for fusing the toner image to its supporting surface be positioned beneath the path along which the support travels. Although fusing of the toner image can be accomplished by heating the rear surface of the supporting sheet to a temperature sufficient to liquify the toner supported on the front surface, it is usually preferred to subject the toner directly to the thermal source. This means that, in machines where the fusing station is positioned beneath the path along which the toner-bearing support travels, the support will be traveling with its toner-bearing surface facing downward toward the fusing station. Because the toner, prior to fusing, adheres to the support surface solely by electrostatic forces, there is a tendency for the toner to become detached from the supporting surface and fall under the force of gravity upon machine elements lying below. Moreover, in addition to toner dropoff, whenever a paper-receiving sheet is used, there is a tendency for paper fibers to become detached from the sheet and descend upon machine elements, thereby contaminating the same. Such dropoff of particulate material from the toner support sheet has heretofore presented a problem in maintaining the fusing station operable for extended periods of time. Dropoff of particulate material into the fusing station eventually produces a film of dirt on the source of thermal energy, and any associated reflective elements which serve to direct energy from the source toward the region where fusing takes place. When the film of dirt increases to such intensity as to render the thermal source incapable of providing sufficient energy to achieve fusing, the electrophotographic apparatus must be shut down in order to effect a cleaning operation.

In accordance with the present invention, means are provided for preventing particulate material, such as toner, paper fiber, etc, which becomes detached from a toner-bearing surface traveling along a predetermined path within an electrophotographic apparatus from contacting the elements comprising the fusing station and thereby contaminating the same. According to a preferred embodiment, apparatus is provided for generating an air curtain between the toner-bearing surface and the fusing station whereby such particulate material may be intercepted shortly after becoming detached from the surface and displaced to a position removed from the environment of the fusing station. Preferably, a stream of air under a predetermined pressure is directed from a point on the upstream side of the fusing station along a path parallel to that along which the toner-bearing surface travels. Positioned on the opposite side of the fusing station, downstream therefrom and in a position to intercept the airstream, is an opening to a vacuum chamber. By balancing the flow'of positive air pressure inflow with the negative pressure exhaust provided by the vacuum chamber, a protective air curtain may be formed which, while maintaining the fusing station free of contaminants, offers no adverse effects on fusing efficiency. The invention, and its ob.- jects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below.

The invention will be better understood from the following more detailed description taken in conjunction with the accompanying drawing which shows schematically the basic arrangement of the invention as incorporated in an electrophotographic copying apparatus.

Referring now to the drawing, an electrophotographic copier embodying the invention is shown to comprise an endless photoconductive belt 2, driven about rollers 3 and 4 along a predetermined path by motor 5 which is operably coupled with one of the rollers. Disposed along the path are the various electrophotographic stations which serve to form a toner image of the document being reproduced on the outer surface of belt 2. As belt 2 passes charging station 6, its outer surface receives a uniform electrostatic charge from a corona source or the like. Upon being uniformly charged, the belt is advanced past an exposure station 7 where it is imagewise exposed to actinic radiation in accordance with the light and dark areas of the original document, Such imagewise exposure serves to selectively dissipate the uniform charge on the belt to form an electrostatic latent image corresponding to the original document. Development of the electrostatic image is accomplished as belt 2 is advanced past development station 8. The latter generally comprises a reservoir of electrostatic toner particles 9 and means for applying the particles to the electrostatic image. By

employing appropriately charged toner particles, it is possible to produce a positive or negative toner image of the original document. In order to subsequently use that portion of the photoconductive belt bearing the toner image, the toner image is transferred to a paper receiving sheet 11 onwhich the toner image can be permanently fused. Such a transfer is commonly effected by a paper feeding device 12 which feeds sheets of paper from a paper supply 13 to a transfer station 14 simultaneously. with the passage therepast of the tonerbearing belt 2. A shift register R serves to control the timing of the electrophotographic operations and-to synchronize the feeding of the paper receiving sheets with the movement of the photoconductive belt. The

shift register R includes a rotatable segmented and slotted cylinder 20 which is driven by suitable means, such as belt 22, extending from a pulley around roller 3 so that movement of the. shift register is in direct response to movement of the photoconductive belt 2.

Transfer station 14 commonly comprises means for electrostatically charging the paper receiving sheet so as to attract toner particles from belt 2 thereto. After the toner image is transferred to the paper receiving sheet, the sheet is peeled away from the beltas the latter passes over small roller 4. The toner-bearing receiving sheet is then fed to a fusing station 30 where the toner image is permanentized.

Fusing station 30 comprises an endless mesh belt transport 31 which travels about rollers 32 and 33. Belt 31 can be drivenin a clockwise direction and at the same speed as belt 2-by connecting the axles of rollers 33 and 4 with belt 35 in the manner shown. The paper receiving sheet with its toner-bearing surface facing downward is caused to adhere to transport 31 by the suction produced by a vacuum source disposed on the rear surface of the lower leg of the transport. Such a vacuum transport is disclosed in US. Pat. No. 3,498,592 issued to Moser et a].

Disposed vertically beneath the vacuum transport 31 is the apparatus which embodies the invention. Such apparatus includes means for fusing the toner particles to the paper receiving sheet, such as an infrared lamp 40 and reflector 41, and means for producing a stream of air or air curtain 42 substantially parallel to the path along which the toner-bearing receiving sheet travels as it passes directly above the fusing device. The last-mentioned means comprises means defining a pair of plenum chambers 43 and 44 wherein equal but opposite pressures are maintained. The phrase equal but opposite as used herein refers to the plenum chamber pressures using the ambient pressure, such as the pressure in the region 45 intermediate the plenum chambers, as a standard. Thus, for example, should the ambient pressure be 15.0 p.s.i., then the pressures in chambers 43 and 44 might be l7.0 and 13.0 p.s.i., respectively. Chambers 43 and 44 are provided with communicating slot apertures 46 and 47, respectively, each of which has a width equal to or greater than the width of the paper receiving sheet. The equal but opposite pressures in chambers 43 and 44 are maintained by a fan 49 disposed in a conduit 50 connecting the chambers. Disposed on the negative pressure side of conduit 50 between fan 49 and chamber 44-is a filter 51 having an active element adapted to trap particles of a size comparable to toner particles.

In operation, the toner-bearing receiving sheet with its toner-bearing surface facing downward is advanced on the lowermost surface of transport 31 overtop infrared lamp 40. Since the toner particles adhere to the paper receiving sheet only by electrostatic attraction, there is a tendency for the toner particles to become disassociated from the receiving sheet and to fall under the force of gravity upon the lamp 40 and itsassociated reflector 41. Moreover, since the receiving sheet is usually comprised of fibrous material, there is a ten dency for paper fibers to become "detached and to fall upon the fusing apparatus. In this manner the infrared lamp and its reflector can become contaminated and are thereby less efficient in-producing fusion between the toner particles and the receiving sheet. In accordance with the invention, an air curtain 42 is provideddirectly above lamp 40. The air curtain serves to intercept particles falling from the paper receiving sheet and to transport them through conduit 50 to filter 51 wherein they are trapped and may be readily disposed of. It is important that the pressures in chamber s 43 and 44 be maintained substantially equal. If the positive air flow from chamber 43 is. substantially greater than the negative flow into chamber 44, the air curtain will tend to blow the paper from the transport 31 and also disturb the loose toner particles on the ,unfused print. On the other hand, if the negative pressure in chamber 44 is substantially greater than the positive pressurein chamber 43, the paper receiving sheet is likely to be pulled off the vacuum transport by suction. After the toner image is fused to the paper receiving sheet, the sheet is deposited in a receptacle 60.

While the invention has been disclosed with particular reference to an electrophotographic copier having a configuration in which the toner-bearing support passes above the fusing elements of the fusing station in an inverted position, that is with itstoner-bearing surface facing downward toward the fusing elements, it is quite apparent that the utility of the invention is neither dependent upon the relative positions of the fusing station and the support, nor on the orientation of the sup port. So long as there is any likelihood of particulate material or other contaminates becoming detached,

from'the receiving sheet, the protective air curtain of the invention will sufficiently isolate the fusing station from the receiving'sheet as to prevent such material from reaching the fusing elements.

The invention has been described in detail with particular reference to a preferred embodiment thereof,

but it will be understood that variations and modifica 'as to intersect a plane extending upwardly from said source, and means for displacingfrom said energy source particulate material, falling from the support under the force of gravity toward said energy source, whereby contamination of said energy source is avoided.

2. The invention'according to claim 1 wherein said displacing means is positioned intermediate said path defining means and said source.

3. The invention according to claim 2 wherein said displacing means comprises means for producing a curtain of fluid extending substantially parallel to said path at the line said path intersects said plane.

4. The invention according to claim 3 wherein said fluid is essentially air.

5. The invention according to claim 3 wherein said fluid curtain producing means comprises a source of fluid pressure, means defining a first aperture on one side of said plane, first conduit means operatively connecting said fluid source with said first aperture, means defining a second aperture opposite said first aperture on the other side of said plane, means for producing a negative pressure having an absolute value substantially equal to said positive pressure, and second conduit means operatively connecting said second aperture with said negative pressure producing means.

6. The invention according to claim 5 further comprising filtering means disposed in said second conduit means for entrapping the particulate material carried by the fluid in said second conduit.

7. Apparatus for fusing thermoplastic particles to a supporting surface while such surface moves along a predefined path, said apparatus comprising means for liquifying the thermoplastic particles and means for generating a protective gas-curtain between said path and said liquifying means, said gas-curtain generating means comprising a first plenum chamber containing gas under a predetermined positive pressure and means defining an aperture in said first chamber for directing a curtain of gas substantially parallel to said path, whereby particulate material given off by said surface in a direction toward said liquifying means is displaced from the vicinity of said liquifying means.

8. The invention according to claim 7 further comprising a second plenum chamber containing gas under a negative pressure substantially equal in magnitude to said predetermined positive pressure, and means defin ing an aperture in said second chamber for receiving said curtain of gas, said first and second chambers being positioned on opposite sides of said liquifying means, between said liquifying means and said predetermined path. 

1. Apparatus for fusing a resinous powder image onto a movable support surface on which the image has been formed, said apparatus comprising a source of thermal energy, means defining a path along which the support is guideable, at least a portion of said path being spaced from and positioned over said source so as to intersect a plane extending upwardly from said source, and means for displacing from said energy source particulate material, falling from the support under the force of gravity toward said energy source, whereby contamination of said energy source is avoided.
 2. The invention according to claim 1 wherein said displacing means is positioned intermediate said path defining means and said source.
 3. The invention according to claim 2 wherein said displacing means comprises means for producing a curtain of fluid extending substantially parallel to said path at the line said path intersects said plane.
 4. The invention according to claim 3 wherein said fluid is essentially air.
 5. The invention according to claim 3 wherein said fluid curtain producing means comprises a source of fluid pressure, means defining a first aperture on one side of said plane, first conduit means operatively connecting said fluid source with said first aperture, means defining a second aperture opposite said first aperture on the other side of said plane, means for producing a negative pressure having an absolute value substantially equal to said positive pressure, and second conduit means operatively connecting said second aperture with said negative pressure producing means.
 6. The invention according to claim 5 further comprising filtering means disposed in said second conduit means for entrapping the particulate material carried by the fluid in said second conduit.
 7. Apparatus for fusing theRmoplastic particles to a supporting surface while such surface moves along a predefined path, said apparatus comprising means for liquifying the thermoplastic particles and means for generating a protective gas-curtain between said path and said liquifying means, said gas-curtain generating means comprising a first plenum chamber containing gas under a predetermined positive pressure and means defining an aperture in said first chamber for directing a curtain of gas substantially parallel to said path, whereby particulate material given off by said surface in a direction toward said liquifying means is displaced from the vicinity of said liquifying means.
 8. The invention according to claim 7 further comprising a second plenum chamber containing gas under a negative pressure substantially equal in magnitude to said predetermined positive pressure, and means defining an aperture in said second chamber for receiving said curtain of gas, said first and second chambers being positioned on opposite sides of said liquifying means, between said liquifying means and said predetermined path. 